Wollastonite crystallized glass for artificial tooth and method for coloring same

ABSTRACT

Disclosed are a wollastonite crystallized glass for an artificial tooth and a method for coloring same, the method enabling a production of a uniform shade without degrading the physical properties of a crystallized glass by means of simply adding a small amount of coloring additive powder when preparing the crystallized glass.

TECHNICAL FIELD

The present disclosure relates to a wollastonite-based crystallized glass for an artificial tooth and a method for coloring the same. More particularly, the present disclosure relates to a wollastonite-based crystallized glass for an artificial tooth and a method for coloring the same, in which in a production of the crystallized glass, addition of a small amount of coloring additive powders allows a uniform shade to be rendered without degrading properties of the glass.

BACKGROUND

Since natural tooth shades vary considerably depending on races or ages, it is very important to accurately adapt artificial tooth shades to the natural tooth shades of patients. At present, stabilized zirconia widely used as the artificial tooth has a low light transmittance and thus is poorly aesthetic. Further, the stabilized zirconia has its own shade, which makes it difficult to adapt the shade thereof to the natural tooth shade.

For this reason, lithium disilicate crystallized glass has been recently used because the lithium disilicate crystallized glass has a suitable visible light transmittance and thus is superior in aesthetics, and has excellent mechanical properties. However, because the lithium disilicate crystallized glass has an inherent shade, it may be difficult to render and control the shade thereof.

Recently, efforts have been made to study a novel crystallized glass for an artificial tooth in a current situation where the crystallized glass for the artificial tooth is substantially limited to the lithium disilicate based crystallized glass.

As Related Prior art, Korean Patent Application Publication No. 10-2014-0063526 (published on May 27, 2014) describes a doping or coloring method of ceramics, glass ceramics, or glasses.

In the Prior Art as described above, a solution containing a coloring element is produced (by dissolving a corresponding metal salt into a corresponding solvent), and then is sprayed. However, in this approach, there is a disadvantage that a production step is further added, and a shade is likely to be rendered unevenly.

DISCLOSURE Technical Purposes

A purpose of the present disclosure is to provide a wollastonite-based crystallized glass for an artificial tooth and a method for coloring the same in which the glass meets mechanical properties needed to be used as the artificial tooth, and when the glass has been crystallized, the glass renders a bright white, thereby to allow shade render and control of the artificial tooth to be easy.

Technical Solutions

In one aspect of the present disclosure, there is provided a method for coloring a wollastonite-based crystallized glass for an artificial tooth, the method comprising: (a) drying, weighing and ball-milling raw glass powders and coloring additive powders, wherein the raw glass powders includes SiO₂, CaO, CaF₂ and Na₂O; (b) introducing the ball-milled raw glass powders and coloring additive powders into a furnace, and calcining the powders therein at 950 to 1050° C. for 1 to 3 hours, and then cooling the powders to a room temperature; (c) melting the calcined powders to form a glass; (d) introducing the glass into a preheated mold at 450 to 550° C., preforming a thermal-stress removal heat-treatment of the glass at 450 to 550° C. for 1 to 3 hours, and cooling the glass to a room temperature; and (e) preforming a two-steps crystallization heat-treatment of the glass and then cooling the glass to a room temperature to form a crystallized glass, wherein the two-steps crystallization heat-treatment includes a first heat-treatment of the glass at a nucleation temperature, and a second heat-treatment of the glass at a crystallization temperature.

In another aspect of the present disclosure, there is provided a wollastonite-based crystallized glass for an artificial, wherein the wollastonite-based crystallized glass is colored to have a shade of one of groups A, B, C, or D of a Vita shade guide as a tooth shade reference, wherein the wollastonite-based crystallized glass has a wollastonite crystal phase as a main phase and has a calcium fluoride silicate crystal phase as an additional phase.

Technical Effects

In accordance with the wollastonite-based crystallized glass for the artificial tooth and the method for coloring the same according to the present disclosure, in the production of the crystallized glass for the artificial tooth, the coloring may be achieved by simply adding a small amount of the coloring additive powders to the raw glass powders, thereby rendering a uniform shade of the crystallized glass without degrading its inherent properties. Thus, the wollastonite-based crystallized glass may be used to perform coping and crowning of the artificial tooth.

As a result, the wollastonite-based crystallized glass for the artificial tooth as produced by the method in accordance with the present disclosure may be colored to have a shade of one of groups A, B, C, or D of the Vita shade guide as a tooth shade reference. The wollastonite crystallized glass has a wollastonite crystal phase as a main phase and has a calcium fluoride silicate crystal phase as an additional phase.

Further, the wollastonite-based crystallized glass for the artificial tooth as produced by the method in accordance with the present disclosure may exhibit a Vickers hardness 6.0 to 6.5 GPa, a fracture toughness 2.0 to 2.5 MPa·m⁻², a flexural strength 250 to 320 MPa and a 1 mm thickness-based visible-light transmittance 35 to 50%.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a process flow diagram showing a coloring method of a wollastonite-based crystallized glass for an artificial tooth according to an embodiment of the present disclosure.

FIG. 2 shows the Vita shade guide as a tooth shade reference.

FIG. 3 shows a specimen before and after a crystallization heat-treatment according to Present Examples 1 to 9.

FIG. 4 shows a specimen before and after a crystallization heat treatment according to Present Examples 10 to 18.

FIG. 5 shows a specimen before and after a crystallization heat treatment according to Present Examples 19 to 28.

FIG. 6 is a graph showing XRD measurement results of a specimen according to Present Example 1.

DETAILED DESCRIPTIONS

Advantages and features of the present disclosure, and methods to accomplish the advantages and features will become apparent with reference to embodiments, which is described in detail below with reference to the accompanying drawings. However, the present disclosure may not be limited to the embodiments as described below, but may be embodied in various different forms. The embodiments only makes the present disclosure complete and may be provided to fully set forth the scope of the present disclosure to those skilled in the art. The present disclosure is only defined by the scope of the claims. Like reference numerals refer to like elements herein.

Hereinafter, a wollastonite-based crystallized glass for an artificial tooth and a method for coloring the same according to preferred embodiments of the present disclosure will be described in detail with reference to the accompanying drawings.

FIG. 1 is a process flow diagram showing a method for coloring a wollastonite-based crystallized glass for an artificial tooth according to an embodiment of the present disclosure.

Referring to FIG. 1, a method for coloring a wollastonite-based crystallized glass for an artificial tooth according to an embodiment of the present disclosure may include a drying and ball-milling step S110, a calcination step S120, a melting step S130, a thermal-stress removal heat-treatment step S140, and a crystallization heat-treatment step S150.

Driving and Ball-Milling

The drying and ball-milling step S110 may dry raw glass powders including SiO₂, CaO, CaF₂ and Na₂O, and coloring additive powders, weigh the dried powders and ball-mill the dried powders.

In this connection, the drying may be carried out to remove moisture from the raw glass powders and coloring additive powders. The drying is preferably carried out at 100 to 150 degrees C. for 30 to 120 minutes.

These raw glass powders may be composed of mixed powders including SiO₂, CaO, CaF₂ and Na₂O in order to produce the crystallized glass having a wollastonite crystal phase having a chemical composition [CaSiO₃] as a main phase.

More specifically, the raw glass powders preferably have a composition of 51 to 57% by weight of SiO₂, 25 to 31% by weight of CaO, 11 to 16% by weight of CaF₂ and 3 to 7% by weight of Na₂O.

SiO₂ serves to form a glass network structure and is a main component of the wollastonite crystal phase. It is preferable that such SiO₂ is added at a content of 51 to 57% by weight based on the total weight of the raw glass powders. When the addition amount of SiO₂ is smaller than 51% by weight, the wollastonite crystal phase may not be formed and excessive crystallization may lower the light transmittance of the glass. On the contrary, when the addition amount of SiO₂ exceeds 57% by weight, the crystallization does not proceed well, and, especially, the wollastonite crystal phase may not be formed, and strength and toughness of the resulting glass may be insufficient.

CaO is a main component of the wollastonite crystal phase and is preferably added in a content of 25 to 31% by weight based on the total weight of the raw glass powders. When the amount of CaO as added is smaller than 25 wt %, the wollastonite crystal phase may not be formed. On the other hand, when the amount of CaO added exceeds 31% by weight, the strength of the glass may be insufficient.

CaF₂ is a main component of the wollastonite crystal phase and is added for exhibiting a effect of preventing dental caries and inhibiting microbial propagation. It is preferable that such CaF₂ is added at a content of 11 to 16% by weight based on the total weight of the raw glass powders. When the added amount of CaF₂ is smaller than 11% by weight, the wollastonite crystal phase may be hardly formed, and dental caries prevention and microbial growth inhibition may not be realized. On the contrary, when the amount of CaF₂ added exceeds 16% by weight, this raises the production cost, which is not economical.

Na₂O improves a melting ability during melting for glass formation and plays a role in promoting the formation of the wollastonite crystal phase. Na₂O is preferably added in a content of 3 to 7% by weight based on the total weight of the raw glass powders. When the amount of Na₂O added is smaller than 3% by weight, the addition amount is insignificant, thus, to make it difficult to form the wollastonite crystal phase. On the other hand, when the amount of Na₂O added exceeds 7% by weight, the strength of the glass may be lowered.

FIG. 2 shows the Vita shade guide as a tooth shade reference.

Referring to FIG. 2, coloring additive powders are preferably added such that the resulting glass is colored to have one of the shades in groups A, B, C and D of the Vita shade guide as a tooth shade reference while not degrading the properties of the glass.

In a comparison example, the wollastonite-based crystallized glass for the artificial tooth may be produced by crystallization heat-treatment of only the raw glass powders without the coloring additives. In this case, the crystallized glass renders a bright white color. To the contrary, in accordance with the present disclosure, the coloring may be achieved by simply adding a small amount of the coloring additive powders to the raw glass powders. In this case, the crystallized glass for the artificial tooth may exhibit uniform shade rendering and thus excellent aesthetics without deteriorating the inherent physical properties thereof.

Thus, in the method for coloring the wollastonite-based crystallized glass for an artificial tooth according to an embodiment of the present disclosure, the coloring is performed by directly mixing the coloring additive powders with the raw glass powders and then by melting the mixture. Thus, not only a separate process such as a spray coating may be omitted, but also a uniform shade may be rendered.

Such coloring additive powders may include an oxide of at least one selected from a group consisting of Er, Fe, Cr, Mn, V, Cu, and Ce. More concretely, the oxide may include at least one selected from a group consisting of Er₂O₃, Fe₂O₃, Cr₂O₃, Mn₂O₃, V₂O₅, CuO and CeO₂.

In this connection, the coloring additive powders are preferably added in an amount of 0.001 to 5 parts by weight based on 100 parts by weight of the raw glass powders. When the amount of the coloring additive powders as added is smaller than 0.001 part by weight based on 100 parts by weight of the raw glass powders, the addition amount thereof is insufficient, thereby to make it difficult to exhibit the coloring effect properly. On the contrary, when the addition amount of the coloring additive powders exceeds 5 parts by weight with respect to 100 parts by weight of the raw glass powders, this may raise the production cost without increasing the coloring effect, and may cause a problem of deteriorating the mechanical properties of the crystallized glass.

Calcination

In the calcination step S120, ball-milled raw glass powders and coloring additive powders are put into a furnace, then calcined at 950 to 1050° C. for 1 to 3 hours, and then cooled to a room temperature.

When the mixture powders are calcined at 950 to 1050° C. for 1 to 3 hours, organic components as an impurity may be burned and discharged to the outside, and carbon dioxide gas may be generated and discharged to the outside.

When the calcination temperature is lower than 950° C. or the calcination duration is smaller than 1 hour, the organic component and carbon dioxide are not completely removed and remain. Thus, during subsequent crystallization heat-treatment, the properties of the crystallized glass may be degraded. Conversely, when the calcination temperature exceeds 1050° C. or the calcination duration exceeds 3 hours, this may be a factor that lowers a production yield without further increase in the effect. This is not preferable.

In this connection, the cooling is preferably performed in a cooling-in-furnace manner. When air-cooling or water-cooling is applied, internal stress is severely formed in the glass. In some cases, cracking may occur. Thus, cooling the glass in the furnace is preferable. In this connection, the room temperature may be in a range of 1 to 40° C., but may not be limited thereto.

Melting

In the melting step S130, the calcined powders are melted to form the glass.

In this connection, in the melting step, it is preferable to add the calcined powders to a melting furnace, raise a temperature to 1400 to 1500° C. at a rate of 8 to 12° C./min, and then perform melting at 1400 to 1500° C. for 30 to 120 minutes.

When the temperature rise rate is lower than 8° C./min, the productivity is low because the duration is long. On the other hand, when the temperature rise rate exceeds 12 degrees C./min, the volatilized amount of the raw glass powders and the coloring additive powders is increased, which may act as a factor for lowering the physical properties of the crystallized glass.

In this connection, when the melting temperature is lower than 1400° C. or when the melting duration is smaller than 30 minutes, the raw glass powders and coloring additive powders are not completely melted and a moldability is deteriorated. Conversely, when the melting temperature exceeds 1500° C. or the melting duration exceeds 120 minutes, excessive energy and duration are required, which is not economical.

Thermal-Stress Removal Heat-Treatment

In the thermal-stress removal heat-treatment step S140, the glass is poured into a mold preheated to 450 to 550° C., followed by thermal-stress removal heat treatment at 450 to 550° C. for 1 to 3 hours and then cooled to a room temperature.

In this connection, when the thermal-stress removal heat-treatment temperature is lower than 450° C., or when the thermal-stress removal heat-treatment duration is smaller than 1 hour, it may be difficult to completely remove the thermal stress from the glass. Conversely, when the thermal-stress removal heat-treatment temperature exceeds 550° C. or the thermal-stress removal heat-treatment duration exceeds 3 hours, this may not be economical because this takes excessive energy and duration and further may lead to the formation of unwanted crystal phases.

Crystallization Heat-Treatment

The crystallization heat-treatment step S150 may include preforming a two-steps crystallization heat-treatment of the glass and then cooling the glass to a room temperature to form a crystallized glass. The two-steps crystallization heat-treatment includes a first heat-treatment of the glass at a nucleation temperature, and a second heat-treatment of the glass at a crystallization temperature.

In this connection, the crystallization heat-treatment step may be subdivided into following 2 sub-steps: a nucleation heat-treatment sub-step of heat-treating the glass at 680 to 750° C. for 3 to 8 hours; and a crystallization heat-treatment sub-step that heat-treats the glass at 830 to 900° C. for 8 to 15 hours.

Thus, the two-stage heat treatment consisting of the nucleation heat-treatment sub-step of heat-treating the glass at 680 to 750° C. for 3 to 8 hours, and the crystallization heat-treatment sub-step that heat-treats the glass at 830 to 900° C. for 8 to 15 hours may allow the crystallized glass to be produced in a more stable manner than in a single stage heat treatment.

In this connection, when the crystallization heat-treatment temperature is lower than 830° C. or the crystallization heat-treatment duration is smaller than 8 hours, crystallization may be insufficient due to the incomplete heat-treatment. Conversely, when the second crystallization heat-treatment temperature exceeds 900° C., or when the second crystallization heat-treatment duration exceeds 15 hours, this may cause a problem of deterioration of mechanical properties due to grain growth due to the excessive heat treatment.

In accordance with the method for coloring the wollastonite-based crystallized glass for the artificial tooth according to the present disclosure, in the production of the crystallized glass for the artificial tooth, the coloring may be achieved by simply adding a small amount of the coloring additive powders to the raw glass powders, thereby rendering a uniform shade of the crystallized glass without degrading its inherent properties. Thus, the wollastonite-based crystallized glass may be used to perform coping and crowning of the artificial tooth.

As a result, the wollastonite-based crystallized glass for the artificial tooth as produced by the method in accordance with the present disclosure may be colored to have a shade of one of groups A, B, C, or D of the Vita shade guide as a tooth shade reference. The wollastonite crystallized glass has a wollastonite crystal phase as a main phase and has a calcium fluoride silicate crystal phase as an additional phase.

Further, the wollastonite-based crystallized glass for the artificial tooth as produced by the method in accordance with the present disclosure may exhibit a Vickers hardness 6.0 to 6.5 GPa, a fracture toughness 2.0 to 2.5 MPa·m⁻², a flexural strength 250 to 320 MPa and a 1 mm thickness-based visible-light transmittance 35 to 50%.

Present Example

Hereinafter, a preferred Present Example is illustrated to help understand the present disclosure. It will be apparent to those skilled in the art that various modifications and variations are possible within the scope and spirit of the present disclosure, and such variations and modifications fall within the scope of the appended claims.

Specimen Production

As specimens, colored crystallized glasses for the artificial tooth according to Present Examples 1 to 28 were produced with compositions and process conditions as indicated in Table 1.

In this connection, according to Present Examples 1 to 28, after the addition of the raw glass powders and coloring additive powders to a drying machine for moisture removal, the mixture was dried at 120° C. for 1 hour therein.

Then, the dried raw glass powders and coloring additive powders were weighed according to the compositions shown in Table 1, and subjected to the dry ball-milling for 24 hours.

Then, the ball-milled raw glass powders and coloring additive powders were sieved and placed in a platinum crucible.

Next, the platinum crucible was charged into an electric furnace for calcination. A temperature of the electric furnace was raised to 1000° C. at a temperature rise rate of 10° C./min. Thereafter, the furnace was maintained at 1000° C. for 1 hour and 30 minutes. Then, the cooling-in-furnace was executed at the room temperature 15 degrees C. to form a glass.

Subsequently, the calcined glass was put into a melting furnace, which was heated to 1450° C. at a temperature rise rate of 10° C./min, and then maintained at 1450° C. for 90 minutes for melting of the glass.

Next, the molten glass was poured into a preheated graphite mold at 500° C. The graphite mold was maintained at 500° C. for 1 hours to perform the thermal-stress removal heat-treatment, and then cooled to the room temperature.

After the crystallization heat treatment of the glass, the colored crystallized glass specimen for the artificial tooth was produced via the cooling-in-fumace to the room temperature.

In this crystallization heat-treatment, for the specimens according to Present Examples 1 to 14, 2 stages heat-treatment was performed as follows: first, for 5 hour and at the nucleation temperature of 720° C.: and, second, for 10 hours and at a crystallization temperature of 870° C.

Further, in this crystallization heat-treatment, for the specimens according to Present Examples 15 to 28, 2 stages heat-treatment was performed as follows: first, for 5 hour and at the nucleation temperature of 700° C.; and, second, for 10 hours and at a crystallization temperature of 850° C.

TABLE 1 crystallization Coloring additive heat-treatment temperature powders (° C.) Raw glass powders Content Nucleation Crystallization Examples (wt %) Type (wt %) temperature temperature Present SiO₂—CaO—CaF₂—Na₂O Fe₂O₃ 0.1 720 870 Example 1 (54.4-27.0-13.3-5.3) Present Fe₂O₃ 0.5 Example 2 Present Er₂O₃ 0.5 Example 3 Present Er₂O₃ 1 Example 4 Present Cr₂O₃ 0.003 Example 5 Present Cr₂O₃ 0.01 Example 6 Present Cr₂O₃ 0.05 Example 7 Present Cr₂O₃ 0.1 Example 8 Present Mn₂O₃ 0.01 Example 9 Present Mn₂O₃ 0.25 Example 10 Present V₂O₅ 0.1 Example 11 Present V₂O₅ 0.5 Example 12 Present CuO 0.05 Example 13 Present CuO 0.1 Example 14 Present SiO₂—CaO—CaF₂—Na₂O Fe₂O₃ 0.1 700 850 Example 15 (54.4-27.0-13.3-5.3) Present Fe₂O₃ 0.5 Example 16 Present Er₂O₃ 0.5 Example 17 Present Er₂O₃ 1 Example 18 Present Cr₂O₃ 0.003 Example 19 Present Cr₂O₃ 0.01 Example 20 Present Cr₂O₃ 0.05 Example 21 Present Cr₂O₃ 0.1 Example 22 Present Mn₂O₃ 0.01 Example 23 Present Mn₂O₃ 0.25 Example 24 Present V₂O₅ 0.1 Example 25 Present V₂O₅ 0.5 Example 26 Present CuO 0.05 Example 27

2. Property Evaluation

Table 2 shows mechanical and optical properties of the colored crystallized glass specimens for the artificial tooth according to Present Examples 1 to 28.

TABLE 2 Visible-light Vickers Fracture flexural transmittance hardness toughness strength (%, 1 mm Examples (GPa) (MPa · m⁻²) (MPa) thick specimen) Present 6.2 2.2 284 42 Example 1 Present 6.1 2.2 286 41 Example 2 Present 6.2 2.2 281 39 Example 3 Present 6.1 2.3 285 39 Example 4 Present 6.2 2.2 284 40 Example 5 Present 6.1 2.3 283 41 Example 6 Present 6.1 2.2 284 41 Example 7 Present 6.1 2.3 285 40 Example 8 Present 6.2 2.3 286 39 Example 9 Present 6.2 2.2 284 40 Example 10 Present 6.1 2.2 283 41 Example 11 Present 6.2 2.3 286 40 Example 12 Present 6.1 2.3 285 39 Example 13 Present 6.2 2.3 283 41 Example 14 Present 6.3 2.4 291 36 Example 15 Present 6.3 2.3 290 37 Example 16 Present 6.4 2.4 292 36 Example 17 Present 6.3 2.3 291 35 Example 18 Present 6.3 2.3 290 37 Example 19 Present 6.2 2.3 293 36 Example 20 Present 6.3 2.4 292 37 Example 21 Present 6.3 2.4 294 37 Example 22 Present 6.4 2.3 291 36 Example 23 Present 6.3 2.4 293 35 Example 24 Present 6.3 2.4 292 37 Example 25 Present 6.4 2.3 293 37 Example 26 Present 6.4 2.4 294 36 Example 27 Present 6.4 2.3 293 35 Example 28

Referring to Table 1 and Table 2, it may be confirmed that for the specimens according to Present Examples 1 to 28, target values of the properties may be satisfied as follows: a Vickers hardness 6.0 to 6.5 GPa, a fracture toughness 2.0 to 2.5 MPa·m⁻², a flexural strength 250 to 320 MPa and a 1 mm thickness-based visible-light transmittance 35 to 50%.

FIG. 3 shows a specimen before and after a crystallization heat-treatment according to Present Examples 1 to 9. FIG. 4 shows a specimen before and after a crystallization heat treatment according to Present Examples 10 to 18. FIG. 5 shows a specimen before and after a crystallization heat treatment according to Present Examples 19 to 28.

As shown in FIG. 3 to FIG. 5, it may be confirmed that, in the specimens according to Present Examples 1 to 28, various shades are rendered depending on the types and contents of the coloring additive powders.

Therefore, it may be confirmed that when a small amount of the coloring additive powders is directly added so as to render the shades of groups A, B, C, and D in the Vita shade guide as a tooth shade reference, the uniform shade rendering of the glass may be realized without sacrificing the inherent properties of the crystallized glass for the artificial tooth.

In this connection, we may see that, in comparison between Present Examples 1 to 14 and Present Examples 15 to 28, the slight shade difference may occur therebetween. This may be attributed to a difference in the crystallization heat-treatment conditions, that is, the nucleation temperature and crystallization heat-treatment temperature.

FIG. 6 is a graph showing XRD measurement results of a specimen according to Present Example 1.

As shown in FIG. 6, in the specimen according to Present Example 1, a large number of wollastonite crystal peaks were observed in the X-ray diffraction phase analysis. Further, some calcium fluoride silicate crystal peaks were observed in the X-ray diffraction phase analysis.

Although the present disclosure has been described with reference to the embodiments of the present disclosure, various changes or modifications may be made in a level of the technician having ordinary knowledge in the technical field to which the present disclosure belongs. These changes and modifications may fall within the scope of the present disclosure unless they depart from the scope of the technical idea provided by the present disclosure. Accordingly, the scope of the present disclosure should be determined by the claims set forth below. 

1. A method for coloring a wollastonite-based crystallized glass for an artificial tooth, the method comprising: (a) drying, weighing and ball-milling raw glass powders and coloring additive powders, wherein the raw glass powders includes SiO₂, CaO, CaF₂ and Na₂O; (b) introducing the ball-milled raw glass powders and coloring additive powders into a furnace, and calcining the powders therein at 950 to 1050° C. for 1 to 3 hours, and then cooling the powders to a room temperature; (c) melting the calcined powders to form a glass; (d) introducing the glass into a preheated mold at 450 to 550° C., preforming a thermal-stress removal heat-treatment of the glass at 450 to 550° C. for 1 to 3 hours, and cooling the glass to a room temperature; and (e) preforming a two-steps crystallization heat-treatment of the glass and then cooling the glass to a room temperature to form a crystallized glass, wherein the two-steps crystallization heat-treatment includes a first heat-treatment of the glass at a nucleation temperature, and a second heat-treatment of the glass at a crystallization temperature.
 2. The method of claim 1, wherein in (a), the weighing includes weighing the raw glass powders to have a composition of 51 to 57% by weight of SiO₂, 25 to 31% by weight of CaO, 11 to 16% by weight of CaF₂ and 3 to 7% by weight of Na₂O.
 3. The method of claim 1, wherein in (a), the coloring additive powders includes at least one selected from a group consisting of Er₂O₃, Fe₂O₃, Cr₂O₃, Mn₂O₃, V₂O₅, CuO and CeO₂.
 4. The method of claim 1, wherein in (a), the coloring additive powders are added in a content of 0.001 to 5 parts by weight based on 100 parts by weight of the raw glass powders.
 5. The method of claim 1, wherein in (c), the melting includes increasing the calcined powders to 1400 to 1500° C. at an increase rate of 8 to 12° C./min, and then performing melting of the powders at 1400 to 1500° C. for 30 to 120 minutes.
 6. The method of claim 1, wherein in (e), the two-steps crystallization heat-treatment includes: a first heat-treatment in which the glass is heat-treated at a nucleation temperature of 680 to 750° C. for 3 to 8 hours; and a second heat-treatment in which the glass is heat-treated at a crystallization temperature of 830 to 900° C. for 8 to 15 hours.
 7. A wollastonite-based crystallized glass for an artificial tooth produced by the method of claim 1, wherein the wollastonite-based crystallized glass is colored to have a shade of one of groups A, B, C, or D of a Vita shade guide as a tooth shade reference, wherein the wollastonite-based crystallized glass has a wollastonite crystal phase as a main phase and has a calcium fluoride silicate crystal phase as an additional phase.
 8. The wollastonite-based crystallized glass of claim 7, wherein the wollastonite-based crystallized glass exhibits a Vickers hardness 6.0 to 6.5 GPa, a fracture toughness 2.0 to 2.5 MPa·m⁻², a flexural strength 250 to 320 MPa and a 1 mm thickness-based visible-light transmittance 35 to 50%. 